Nature uses covalent modification of biological macromolecules as a fundamental mode of regulation. Designed duplication of this powerful strategy could revolutionize therapeutic development. The transglutaminase reaction provides a suitable vehicle for this, modifying small molecules, peptides and proteins in living systems. It joins amide and amine substrates, and requires no exogenous cofactors or coupled reactions. Natural transglutaminases are promiscuous, calcium-activated, difficult to mass-produce, or unstable, making them unsuitable for targeted use in vivo. Design of novel enzymes, protein binders with near-natural affinity levels, and even novel protein folds have all been achieved. Here, I will integrate these methodologies to develop a transglutaminase enzyme. This enzyme will modify and inactivate the stem cell factor receptor c-Kit, a proven cancer therapeutic target located on the surface of many tumor cells. This specific, covalent modification would reduce the concentration required for efficacy over noncovalent methods, resulting in lower cost and improved safety. This work will explore the nuances of enzyme catalysis and the relationship between fold and function. It provides a novel tool for the diagnostic and therapeutic study of biological systems, and a starting point for the design of new proteins which harness the power of covalent biomolecular modification.